Returning to West Germany, Horkheimer presented his inaugural speech for the reopening of the institute on 14 November 1951, and one week later inaugurated the academic year as a new rector of Frankfurt University. Nevertheless what was once a lively intellectual community became a small team of a few but very busy people, with Horkheimer involved in the administration of the university and Adorno occupied with different projects and teachings. In addition, due to the maintenance of US citizenship, Adorno had to go back to California, where he earned his living from qualitative analysis research. From his side, Horkheimer attempted to attract back his former assistant Marcuse when the opportunity arose for a successor to Gadamer’s chair in Frankfurt, but neither this initiative nor further occasions were successful. Marcuse remained in the United States and was offered a full position by Brandeis University. Adorno returned to Germany in August 1953 and was soon involved again in empirical research combining quantitative and qualitative methods in the analysis of industrial relations for the Mannesmann Company. Then in 1955, he took over Horkheimer’s position as director of the Institute for Social Research, and on 1 July 1957 he was appointed full professor in philosophy and sociology. Adorno’s most innovative contribution was thought to be in the field of music theory and aesthetics, where some of his significant works included Philosophy of Modern Music (1949) and later “Vers une Musique Informelle”. In 1956 Horkheimer retired just as several important publications emerged, such as Marcuse’s Eros and Civilization and the essay collection Sociologica . These events gave character to the precise research phase reached by the “Frankfurt School” and “Critical Theory”.